Copper oxide rectifier



Nov. 20, 1945. C. Q HEIN FAL 5 2,389,363

4 COPPER oxDE REGTIFIER Filed Aug. 23, 1941 Patented Nov. 20, 1945 UNITED STATES PATENT OFFICE correa oxma nEc'rmEa Carl C. Hein, Forest Hills, and John W. Stevenhagen, Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 23, 1941, Serial No. 408,056

` (Cl. 17a-366) 3 Claims.

Our invention relates to methods of improving the performance of copper oxide rectifiers and, in particular, relates to methods of improving the performance of copper. oxide rectifiers which have been heated in a high vacuum for a substantial period prior to oxidationof the copper.

, One object of our' invention is to increase the power output which a copper oxide rectifier of a given size is capable of delivering to a load.

Another object of our invention is to decrease the electrical resistance and heating in the rectier when current is flowing in the normally conductive direction therethrough.

Other objects of our invention will become apparent upon reading the following description taken in connection with the drawing, in'which:

Figure A1 is a plot showing the resulting per'- Aformance of copper oxide rectifiers which have been oxidized without a preliminary high-vacuum treatment and have then been annealed'for two diiferent specified periods; and

Fig. 2 is a plotted curve representing the performance of copper oxide rectiers which have been heated in high vacuum for a substantial period before oxidation and have then been annealed for two specified periods.

In accordance with the disclosure of Carl C. Hein application, Serial No. 286,613 (Case No. 20,471), filed on or about July 26, 1939, and assigned to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pennsylvania, a greatly improved output capacity is obtained from copper oxide rectifiers of the general type described in Grondahl Patent No. 1,640,335 if, prior to the oxidation process for the copper described in the Grondahl patent, the copper is heated for periods of the order of one to seven hours in a vacuum of the order of or less than 30 microns. All copper oxide rectifiers conduct a small amount of current in the direction in which they are normally non-conductive, but rectifiers processed in accordance with the disclosure of the abovementioned Hein application showing reduction of this so-called "reverse-curren to a small fraction of the value characteristic of rectifiers not vacuum treated beforeoxidation, are found to be capable of rectifying much higher voltages per disk and of supplying loads of much higher power than are rectifiers of the latter type.

We have found that by subjecting rectifiers of the Hein vacuum-treated type to an annealing operation, preferably at a temperature.. ofhthe order of sixteen hours, their resistance to current flow in the forward direction is reduced to a minor fraction of the value shown when no such annealing is employed. At the end of the annealing term, therectiers may be quenched in water. We have further found that, while the application of a similar annealing operation to rectifiers which have not been subjected to the Hein vacuum treatment before oxidation will result in a decrease of resistance to current flow in the forward direction, this-reduction of forward resistance is nowhere near as great for the nonvacuum-treated rectifiers as for theHein vacuumtreated rectifiers. We have further found that.

while current ow in the non-conductive direci tion through the rectifiers is increased in both of the above cases by the annealing operation, the increase is relatively small in the case of the Hein vacuum-treated rectifiers, and several times as largein the case of the rectifiers oxidized without vacuum pretreatment.

'I'he foregoing results are illustrated by Figs. 1

, and 2 of the drawing, in which Fig. 1 shows in full line the volt-ampere characteristic of a copper oxide rectifier produced substantially in accordance with the description in the Grondahl Patent No. 1,640,335 and without subjecting the copper to a preliminary heating in vacuum in accordance with the above-mentioned Hein application. The dotted curve in Fig. 1 shows the alteration in the volt-ampere characteristic of the same rectifier' which results from an anneai at 500 C. for a period of sixteen hours. Abscissae to the right of the zero line represent the voltage drop across the rectifier in its current conductive direction, the ordinates above the zero line representing current flow in amperes through the rectier. The abscissae to the left of the zero point represent voltage impressed across the rec4 tier in its non-conductive direction, while the ordinates below the zero line represent the reverse current in milliamperes flowing through the rectif-ler in its non-conductive direction. It will be noted that, while the sixteen-hour annealproduces an increase of the order of perhaps 20% in the current which will flow through the rectifier in the conductive direction while producing a order of 425 C. afterv oxidation, for a period"`cfr the order of hours in duration, this period extending with advantage even up to times ofthe voltage drop therein of .4 of a volt, it more than doubles the reverse current vwhich will :dow through the rectifier in the non-conductive direction under a back voltage of 5 volts.

Fig. 2'represents the volt-ampere characteristics of a rectifier made from the same copper as that represented in Fig. 1, but which has been heat treated in high vacuum in accordance with `it will be seen that with a voltage drop of .4 of

a. volt in the conductive direction, the annealing step increases the current which the rectiier may supply to a load by considerably over 100%. On the other hand, while the reverse current with an impressed voltage in the non-conductive direction of 5 volts is increased, this increase amounts to less than 100% and so is considerably `smaller than the increase in reverse current found in the oase of the rectiers of Fig. 1.

Life tests-.of rectifiers have shown that rectifiers made in accordance with the vacuum treatment process shown in the above-mentioned Hein application and which have been annealed as above described fora sixteen-hour period maintain an e'iciency of between 80% and 84% over a period of five hundred hours, whereas similar rectiers annealed for only fteen minutes drop in efficiency from 80% at the beginning of the test period to some 69% afterve hundred hours. The sixteen-hour anneal period thus obviously both increases the electrical eiliciency of the rectifier and maintains it more constant throughout its life period.

While we have mentioned an anneal at 425 C. as a specific instance of a temperature to be used, annealing at any temperature Vthroughout the range between 1000 C. and room temperature is aasases within the purview of .our invention. We have likewise found that annealing for periods 3f/considerably under sixteen hours still produces a substantial improvement and, accordingly, an'- neaiing for periods of both less than sixteen hours and greater than sixteen hours is within the scope of our present disclosure.

In accordance with the patent statutes, we

have disclosed a particular process for carrying' out our invention, but it will be obvious to those skilled in the art that its principles are of broader application and by no means limited tothe specific values which .we have used as illustrations.

We claim as our invention:

1 The method of improving the electrical characteristics oi' copper oxide rectiers in which the copper blancs have been subjected to heating in high vacuum before oxidation which consists in annealing the rectier elements subsequent to oxidation, andai: a temperature of the order of 425 C. for a period of the order of sixteen hours.

2. 'lhe method of producing copper oxide rectiers which comprises heating the mother copper to a temperature above 500 C. for a. substantial period in a, high vacuum, oxidizing the copper `at a temperature .above 900 C., annealing the CARL C. HEIN. JOHN W. STEVENHAGE'N. 

